Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

2. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

3. For obtaining high COP, the pressure range of compressor should be

Any value

Low

High

Optimum

4. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

5. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

1: 1

1: 9

9: 1

6. Freon group of refrigerants are

Non-inflammable and toxic

Inflammable

Toxic

Nontoxic and non-inflammable

7. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

8. Highest temperature encountered in refrigeration cycle should be

Above critical temperature

Much below critical temperature

Near critical temperature of refrigerant

At critical Temperature

9. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Piston type reciprocating

Centrifugal

10. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Wet vapour

Saturated liquid

Superheated vapour

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11. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-56.6°C

-77.7°C

12. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant pressure

Takes place at constant temperature

Involves no change in volume

Takes place at constant entropy

13. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Relative humidity

Dew point temperature

Dry bulb temperature

14. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

15. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

16. Which of the following cycles uses air as the refrigerant?

Ericson

Bell Coleman

Stirling

Carnot

17. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

18. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Any one of the above

Equal to unity

19. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect vapours

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

20. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Dew point temperature of air

Ambient air temperature

Wet bulb temperature of air

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21. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Zero

Negative

22. In a lithium bromide absorption refrigeration system

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

23. Critical temperature is the temperature above which

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

Water will evaporate

24. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

25. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

1.33

3.33

4.33

2.33

26. Which of the following is not a desirable property of a refrigerant?

Low boiling point

High risibility with oil

Good electrical conductor

Large latent heat

27. The capillary tube, as an expansion device, is used in

Water coolers

Room air conditioners

Domestic refrigerators

All of these

28. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

29. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

30. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.376

0.6

0.4

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31. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Normal cooling

Super-cooling

None of these

Sub-cooling or under-cooling

32. Most thermostatic expansion valves are set for a superheat of

15°C

10°C

20°C

5°C

33. In a refrigeration system, the expansion device is connected between the

Receiver and evaporator

Evaporator and compressor

Compressor and condenser

Condenser and receiver

34. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Carbon dioxide

Brine

Freon

35. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

36. In a refrigeration system, heat absorbed in comparison to heat rejected is

More for small capacity and less for high capacity

Same

Less

37. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

38. The boiling point of ammonia is

-33.3°C

-10.5°C

-77.7°C

-30°C

39. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

None of the above

40. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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